Temporomandibular disorders (TMD) are a collective term encompassing conditions affecting the masticatory system resulting in pain and disability. 1 The prevalence of TMD-related pain is about 10 per cent in the adult population. 2 Pain in the pre-auricular areas and/or localised in the masticatory muscles, joint sounds and deviation or restriction of jaw movement are the most common

Temporomandibular disorders (TMD) include a group of musculoskeletal disorders that may involve increased responsiveness of nociceptive neurons in the central nervous system (ie, central sensitization). To test this hypothesis further, this study examined whether, as compared with healthy subjects, patients with chronic TMD have a greater propensity to develop secondary mechanical hyperalgesia-a phenomenon that can be confidently attributed to central sensitization. In this case-control study, we assessed the area of secondary mechanical hyperalgesia induced experimentally by delivering high-frequency electrical stimulation (HFS) to the volar forearm skin in 20 participants with chronic TMD and 20 matched healthy controls. High-frequency electrical stimulation consisted in 12 trains of constant-current electrical pulses (5 mA) delivered at 42 Hz. The area of secondary mechanical hyperalgesia was evaluated 30 minutes after applying HFS. The area of secondary mechanical hyperalgesia induced by HFS was on average 76% larger in the chronic TMD group (M 5 67.7 cm 2 , SD 5 28.2) than in the healthy control group (M 5 38.4 cm 2 , SD 5 14.9; P 5 0.0003). Regarding secondary outcomes, there was no group difference in the intensity of secondary mechanical hyperalgesia, but allodynia to cotton after HFS was more frequent in the chronic TMD group. To the best of our knowledge, this is the first study to show that individuals with chronic TMD have an increased propensity to develop secondary hyperalgesia in a site innervated extratrigeminally. Our results contribute to a better understanding of the pathophysiology of chronic TMD.

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